Lead was the most common contaminant found among the 263 Lower Manhattan apartments the Environmental Protection Agency tested for a range of possible 9/11-related toxins, according to results released on Monday.

Of the 222 apartments E.P.A. contractors tested before and after cleaning, 70, or 31.5 percent, had lead levels before cleaning that exceeded the agency’s conservative benchmark of 25 micrograms per square foot. After cleaning, 16 apartments still had levels of lead above the E.P.A. standard.

E.P.A. spokesperson Mary Mears cautioned that urban environments often have background lead, making it hard to tell whether the lead detected in wipe tests came from the World Trade Center collapse.

“Everybody would love to be able to draw conclusions from this, but you can’t for lead specifically,” Mears said.

The detailed wipe tests were part of the voluntary asbestos cleaning and testing program the E.P.A. announced in May of 2002 in response to the World Trade Center disaster. Just over 3,400 homes received testing and cleaning for asbestos; 263 apartments were randomly selected to receive in-depth sampling for dioxin and 23 elements, including lead and mercury.

Dave Newman, an industrial hygienist with the New York Committee for Occupational Safety and Health, said that the wipe test results raise questions about the extent of lead contamination in Lower Manhattan.

“The data constitute a small sample and therefore may not be representative,” Newman said. “The data however may indicate that there was a larger number of apartments that could have been affected by lead contamination that may not have been tested or cleaned.”

The E.P.A. sent individual results to all apartments that received the wipe testing. The agency did not re-clean the 16 apartments that had elevated post-cleaning levels of lead; instead, officials gave affected residents information on the proper wet-wiping and HEPA vacuuming cleaning methods to use, said E.P.A. spokesperson Bonnie Bellow.

The E.P.A. also told affected residents what to do if they had small children in the home. Children under age seven are most susceptible to lead poisoning, which can cause cognitive deficits and a lowered I.Q.

Compared with the lead levels, a smaller number of apartments were found to have increased dioxin, mercury, and antimony. While the E.P.A. notified all residents of their own results, the agency did not contact the neighbors of people who had elevated levels of lead or other toxins.

“Just because one person in a building had lead exceedences,” Mears said, referring to elevated levels, “That in no shape or form means other people in the building have lead exceedences.”

“But it indicates that they might,” countered Jo Polett, a resident of 105 Duane St., whose apartment was found to contain pre-cleaning lead levels of five times the agency’s health-based benchmark. She said she wished the E.P.A. had conducted outreach in her building, so she wouldn’t have to decide whether to alert her neighbors herself about possible lead hazards.

The presence of lead paint, more prevalent in older buildings, could also influence test results, Mears said. The building at 105 Duane was constructed around 1990, but much of the housing in Lower Manhattan consists of residential conversions built before the 1970s.

The E.P.A. organized the wipe test results by census tracts, or small sections of land used to tally population. There are about 17 census tracts in the E.P.A. testing area south of Canal, Pike, and Allen Sts., but the E.P.A. did not test in two tracts on the southern tip of Manhattan.

In the census tract for Battery Park City, a new development, 12 apartments had elevated lead levels before cleaning. Levels did not go down below the benchmark in 3 of the 12 apartments. Mears said that an E.P.A toxicologist would have to study the Battery Park City results further before she could comment.

In the census tract for Tribeca east of Independence Plaza North, 16 apartments had elevated pre-cleaning levels of lead, a number reduced to 5 after cleaning.

Many factors can contribute to the presence of lead in Lower Manhattan apartments, Bellow said, adding, “Nobody is suggesting there was no lead in the World Trade Center.”

Detailed wipe test results, are available at the E.P.A. Web site at www.epa.gov/wtc